1. Field of the Invention
This invention relates to a biocidal polymer, in particular a biocidal polymer the backbone chain of which is constituted of at least one repeating unit having one or more biocidal functionalities, in particular N-halamine groups, and the preparation process and applications thereof.
2. Description of the Related Art
There have been researchers investigating the preparation of high molecular weight N-halamine polymers. For example, in Journal of Polymer Science: Polymer Chemistry Edition, Vol. 21, pp. 335-340 (1983), A. A. Koutinas and P. G. Demertzis reported the preparation of N-halamine polymers by chlorinating commercial polymers that carry N—H bonds, such as polyamide and polyurea, in which an organic or inorganic hypochlorite was used as a chlorinating agent. It is noted that if a higher degree of chlorination is intended for a polyamide polymer (i.e., more hydrogen atoms at the N—H bonds of the polyamide polymer are to be substituted by a chlorine atom), a more expensive organic reagent, e.g., tert-butyl hypochlorite (t-BuOCl), should be used and a longer reaction is required.
Thereafter, some investigators developed biocidal polymers the backbone chains of which are grafted with cyclic N-halamine units. However, recent researches reveal that while cyclic N-halamine derivatives exhibit excellent biocidal effects and are more stable than free halogen, ozone, and chlorine dioxide, they require more time to exhibit the biocidal effects thereof and have a molecular weight not greater than 200. Therefore, safety concerns may arise when these cyclic N-halamine derivatives are put into practical use.
In addition, referring to Yuyu Sun and Gang Sun (2004), Ind. Eng. Chem. Res., 43:5015-5020, it is noted that whether or not the N—H bonds of a polymer carrying amide bonds can be chlorinated to a N—Cl bond depends on the existence of α-hydrogen next to the amide bond. Referring to Scheme 1, which shows the mechanism of a chlorination reaction where Ar represents an aromatic group and Me represents a methyl group, if there is no α-hydrogen next to the amide bond, formation of the N—Cl bond is possible.

Referring to Scheme 2, if there is α-hydrogen next to the amide bond, it is presumed that the α-hydrogen next to the amide bond will be shifted to the nitrogen atom of the amide bond due to 1,4-hydrogen shift, so that the nitrogen atom cannot be bonded with a chlorine atom to form a N—Cl bond,

In order to understand the biocidal mechanism of compounds carrying amide bonds, in the above-described 2004 article, Yuyu Sun and Gang Sun further performed chlorination to commercial polyamides that carried no α-hydrogen, such as the Kevlar polyamide having repeating units represented by the following formula (p1) and the Nomex polyamide having repeating units represented by the following formula (p2).

Their experimental results reveal that the Nomex polyamide can be continuously chlorinated, whereas the Kevlar polyamide cannot be chlorinated and the chlorination treatment will lead to decomposition thereof. With respect to the observed phenomena, Yuyu Sun et al. proposed that the Keviar polyamide contains weak para-amide bonds linked to the benzene rings, which makes it easier for the Kevlar polyamide to be hydrolyzed during chlorination.
To explain the decomposition of the Kevlar polyamide caused by chlorination, in J. Phys. Chem. B, 111:5581-5586 (2007), S. D. Worley et al., belonging to the same research team of Gang Sun, proposed a reaction mechanism as shown in Scheme 3, which reveals that the chlorinated Kevlar polyamide with contact of water loses one of the chlorine atoms to form a negative charge which, when delocalized, leads to dissociation of the other chlorine to yield a quinone-type structure.

In contrast, when the chlorinated Nomex polyamide is dechlorinated, it is presumed that a stable resonance structure as shown in Scheme 4 will be formed.

In view of the foregoing, it was concluded that two prerequisites may be required for the manufacture of a N-halamine polyamide that exhibits biocidal effects: (1) there is no shiftable α-hydrogen next to the amide bond; and (2) a stable structure will be formed after dechlorination.
Therefore, the research team of S. D. Worley and Gang Sun endeavored to develop cyclic N-halamine polymers that met the above two prerequisites. In fact, in the recent three decades, the research team of S. D. Worley and Gang Sun developed a variety of cyclic N-halamine polymers, including: polymers having side chains grafted with an oxazolidinone of the following formula (p3), polymers having side chains grafted with an imidazolidinone of the following formula (p4), polymers having side chains grafted with a hydantoin of the following formula (p5), etc.,

(wherein Ra1-Ra10 independently represent a C1-C4 alkyl group).
These polymers were subjected to a halogenation treatment so that the hydrogen atom of the N—H bond was substituted by a chlorine atom, thereby rendering the chlorinated polymer to become biocidal. For example, U.S. Pat. No. 5,490,983 discloses 9 cyclic N-halamine biocidal polymers. However, during the preparation of these polymers, the cyclic compounds as described above must be subjected to a preliminary treatment for conversion to a reactive functional group that may be grafted onto the side chain of a selected host polymer. Hence, the preparation processes of these polymers have the disadvantages of complexity in manufacture and limited types of host polymers.
Therefore, there is still a need to develop a new biocidal polymer that exhibits excellent biocidal effects and is easy to fabricate.